The Free On-line Dictionary of Computing (30 December 2018):

network segment

    A part of an Ethernet or other network, on
   which all message traffic is common to all nodes, i.e. it is
   broadcast from one node on the segment and received by all
   others.  This is normally because the segment is a single
   continuous conductor, though it may include repeaters(?).

   Since all nodes share the physical medium, collision
   detection or some other protocol is required to determine
   whether a message was transmitted without interference from
   other nodes.  The receiving node inspects the destination
   address of a packet to tell if it was (one of) the intended
   recipient(s).

   Communication between nodes on different segments is via one
   or more routers.

   (1996-10-16)